As commonly known, in an ultra sonic diagnostic device for medical use provided with an ultra sonic probe comprising minute vibrator groups in an array-form, the scan of an ultrasonic beam is electronically performed. As a device of this kind, an ultrasonic diagnostic device which displays an M mode image as well as a B mode image with a linear scan is actually used.
FIG. 4 is an illustrative representation of a scanning method with which both of these mode images can be obtained. In FIG. 4, minute vibrators 1, 2, . . . 26 are disposed in an array-form. Each of these vibrators is connected to a transmission and reception circuit, not shown in the drawing, through a changeover switch. The minute vibrators, for example, forming groups of 1-5, 2-6, 3-7, 4-8, successively form an opening port for transmitting and receiving ultrasonic waves to perform a scan with the operation of the changeover switch. In other words, the linear scan is executed forming ultrasonic beams (1), (2), (3) and (4) by moving the opening port pitch by pitch in the direction in which the minute vibrators are disposed, and echo signals in individual pitches are collected. After the transmission and reception of the ultrasonic beam (4), the transmission and reception of an ultrasonic beam (5) are performed by a group of minute vibrators 21 to 25, and in this beam position the transmission and reception in a M mode is performed. In the similar way to the above, a linear scan by the groups of minute vibrators 5- 9, . . . 8-12 is performed and the transmission and reception in a M mode is performed by the groups of minute vibrators 21-25, and echo signals in individual pitches are collected. In executing the scan as mentioned above, the imaging of a B mode image or an M mode image of a desired portion can be performed.
In the past, an ultrasonic diagnostic device having such functions as mentioned above is so constituted that a transmission driver with a high voltage control mechanism is provided to each of these vibrators, and a pulse signal from a transmission pulse generator is supplied to the transmission driver for driving a vibrator with a high voltage. In this case, among a plurality of vibrators which constitute an opening port, a vibrator positioned in the center is given the highest voltage, for example, 100 V and a voltage to be given to a vibrator is decreased in proportion to the increase in the distance from the center to the position of a vibrator so that a weighted driving can be performed. Weighting of driving is performed by controlling a high voltage, which is given to each transmission driver as a power supply, with a high voltage control mechanism. In such a case, a high voltage needs a very high speed control such as the change from 0 V to 100 V in 10 .mu.sec to correspond the changeover of the opening port in a linear scan or the changeover between a B mode and an M mode. It causes high cost to have a plurality of transmission drivers with such high speed high voltage control mechanisms. There is also a problem that a high voltage control mechanism produces large quantity of heat because when the voltage is lowered it absorbs a surplus voltage.